process: split routines used to enhance fatal exception stack traces

Previously the enhancement were done right after emitting
`'uncaughtException'`, which meant by the time we knew the
exception was fatal in C++, the error.stack had already been
patched.

This patch moves those routines to be called later during the
fatal exception handling, and split them into two stages:
before and after the inspector is notified by the invocation of
`V8Inspector::exceptionThrown`. We now expand the stack to include
additional informations about unhandled 'error' events before
the inspector is notified, but delay the highlighting of the
frames until after the inspector is notified, so that the
ANSI escape sequences won't show up in the inspector console.

PR-URL: https://github.com/nodejs/node/pull/28308
Fixes: https://github.com/nodejs/node/issues/28287
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

lib/events.js

@@ -25,11 +25,15 @@ const { Math, Object, Reflect } = primordials;
 
 var spliceOne;
 
+const {
+  kEnhanceStackBeforeInspector,
+  codes
+} = require('internal/errors');
 const {
   ERR_INVALID_ARG_TYPE,
   ERR_OUT_OF_RANGE,
   ERR_UNHANDLED_ERROR
-} = require('internal/errors').codes;
+} = codes;
 
 const {
   inspect
@@ -142,8 +146,8 @@ function enhanceStackTrace(err, own) {
     ownStack.splice(off + 1, len - 2,
                     '    [... lines matching original stack trace ...]');
   }
-  // Do this last, because it is the only operation with side effects.
-  err.stack = err.stack + sep + ownStack.join('\n');
+
+  return err.stack + sep + ownStack.join('\n');
 }
 
 EventEmitter.prototype.emit = function emit(type, ...args) {
@@ -162,11 +166,10 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
       er = args[0];
     if (er instanceof Error) {
       try {
-        const { kExpandStackSymbol } = require('internal/util');
         const capture = {};
         // eslint-disable-next-line no-restricted-syntax
         Error.captureStackTrace(capture, EventEmitter.prototype.emit);
-        Object.defineProperty(er, kExpandStackSymbol, {
+        Object.defineProperty(er, kEnhanceStackBeforeInspector, {
           value: enhanceStackTrace.bind(null, er, capture),
           configurable: true
         });

lib/internal/bootstrap/node.js

@@ -299,9 +299,22 @@ process.emitWarning = emitWarning;
 }
 
 function setupPrepareStackTrace() {
-  const { setPrepareStackTraceCallback } = internalBinding('errors');
-  const { prepareStackTrace } = require('internal/errors');
+  const {
+    setEnhanceStackForFatalException,
+    setPrepareStackTraceCallback
+  } = internalBinding('errors');
+  const {
+    prepareStackTrace,
+    fatalExceptionStackEnhancers: {
+      beforeInspector,
+      afterInspector
+    }
+  } = require('internal/errors');
+  // Tell our PrepareStackTraceCallback passed to the V8 API
+  // to call prepareStackTrace().
   setPrepareStackTraceCallback(prepareStackTrace);
+  // Set the function used to enhance the error stack for printing
+  setEnhanceStackForFatalException(beforeInspector, afterInspector);
 }
 
 function setupProcessObject() {

lib/internal/errors.js

@@ -622,6 +622,45 @@ function addNumericalSeparator(val) {
   return `${val.slice(0, i)}${res}`;
 }
 
+// Used to enhance the stack that will be picked up by the inspector
+const kEnhanceStackBeforeInspector = Symbol('kEnhanceStackBeforeInspector');
+
+// These are supposed to be called only on fatal exceptions before
+// the process exits.
+const fatalExceptionStackEnhancers = {
+  beforeInspector(error) {
+    if (typeof error[kEnhanceStackBeforeInspector] !== 'function') {
+      return error.stack;
+    }
+
+    try {
+      // Set the error.stack here so it gets picked up by the
+      // inspector.
+      error.stack = error[kEnhanceStackBeforeInspector]();
+    } catch {
+      // We are just enhancing the error. If it fails, ignore it.
+    }
+    return error.stack;
+  },
+  afterInspector(error) {
+    const originalStack = error.stack;
+    const {
+      inspect,
+      inspectDefaultOptions: {
+        colors: defaultColors
+      }
+    } = lazyInternalUtilInspect();
+    const colors = internalBinding('util').guessHandleType(2) === 'TTY' &&
+                   require('internal/tty').hasColors() ||
+                   defaultColors;
+    try {
+      return inspect(error, { colors });
+    } catch {
+      return originalStack;
+    }
+  }
+};
+
 module.exports = {
   addCodeToName, // Exported for NghttpError
   codes,
@@ -638,6 +677,8 @@ module.exports = {
   // This is exported only to facilitate testing.
   E,
   prepareStackTrace,
+  kEnhanceStackBeforeInspector,
+  fatalExceptionStackEnhancers
 };
 
 // To declare an error message, use the E(sym, val, def) function above. The sym

lib/internal/process/execution.js

@@ -150,10 +150,6 @@ function createOnGlobalUncaughtException() {
     } else if (!process.emit('uncaughtException', er, type)) {
       // If someone handled it, then great. Otherwise, die in C++ land
       // since that means that we'll exit the process, emit the 'exit' event.
-      const { inspect } = require('internal/util/inspect');
-      const colors = internalBinding('util').guessHandleType(2) === 'TTY' &&
-                     require('internal/tty').hasColors() ||
-                     inspect.defaultOptions.colors;
       try {
         if (!process._exiting) {
           process._exiting = true;
@@ -163,14 +159,6 @@ function createOnGlobalUncaughtException() {
       } catch {
         // Nothing to be done about it at this point.
       }
-      try {
-        const { kExpandStackSymbol } = require('internal/util');
-        if (typeof er[kExpandStackSymbol] === 'function')
-          er[kExpandStackSymbol]();
-        er.stack = inspect(er, { colors });
-      } catch {
-        // Nothing to be done about it at this point.
-      }
       return false;
     }
 

lib/internal/util.js

@@ -414,6 +414,5 @@ module.exports = {
   // Used by the buffer module to capture an internal reference to the
   // default isEncoding implementation, just in case userland overrides it.
   kIsEncodingSymbol: Symbol('kIsEncodingSymbol'),
-  kExpandStackSymbol: Symbol('kExpandStackSymbol'),
   kVmBreakFirstLineSymbol: Symbol('kVmBreakFirstLineSymbol')
 };

lib/internal/util/inspect.js

@@ -1683,5 +1683,6 @@ function formatWithOptions(inspectOptions, ...args) {
 module.exports = {
   inspect,
   format,
-  formatWithOptions
+  formatWithOptions,
+  inspectDefaultOptions
 };

src/env.h

@@ -408,6 +408,8 @@ constexpr size_t kFsStatsBufferLength =
   V(crypto_key_object_constructor, v8::Function)                               \
   V(domain_callback, v8::Function)                                             \
   V(domexception_function, v8::Function)                                       \
+  V(enhance_fatal_stack_after_inspector, v8::Function)                         \
+  V(enhance_fatal_stack_before_inspector, v8::Function)                        \
   V(fs_use_promises_symbol, v8::Symbol)                                        \
   V(host_import_module_dynamically_callback, v8::Function)                     \
   V(host_initialize_import_meta_object_callback, v8::Function)                 \

src/inspector_agent.cc

@@ -570,7 +570,7 @@ class NodeInspectorClient : public V8InspectorClient {
     }
   }
 
-  void FatalException(Local<Value> error, Local<Message> message) {
+  void ReportUncaughtException(Local<Value> error, Local<Message> message) {
     Isolate* isolate = env_->isolate();
     Local<Context> context = env_->context();
 
@@ -836,10 +836,11 @@ void Agent::WaitForDisconnect() {
   }
 }
 
-void Agent::FatalException(Local<Value> error, Local<Message> message) {
+void Agent::ReportUncaughtException(Local<Value> error,
+                                    Local<Message> message) {
   if (!IsListening())
     return;
-  client_->FatalException(error, message);
+  client_->ReportUncaughtException(error, message);
   WaitForDisconnect();
 }
 

src/inspector_agent.h

@@ -65,8 +65,8 @@ class Agent {
   void WaitForConnect();
   // Blocks till all the sessions with "WaitForDisconnectOnShutdown" disconnect
   void WaitForDisconnect();
-  void FatalException(v8::Local<v8::Value> error,
-                      v8::Local<v8::Message> message);
+  void ReportUncaughtException(v8::Local<v8::Value> error,
+                               v8::Local<v8::Message> message);
 
   // Async stack traces instrumentation.
   void AsyncTaskScheduled(const v8_inspector::StringView& taskName, void* task,

src/node_errors.cc

@@ -264,38 +264,82 @@ void AppendExceptionLine(Environment* env,
   Abort();
 }
 
-void ReportException(Environment* env,
-                     Local<Value> er,
-                     Local<Message> message) {
-  CHECK(!er.IsEmpty());
-  HandleScope scope(env->isolate());
+enum class EnhanceFatalException { kEnhance, kDontEnhance };
 
-  if (message.IsEmpty()) message = Exception::CreateMessage(env->isolate(), er);
+/**
+ * Report the exception to the inspector, then print it to stderr.
+ * This should only be used when the Node.js instance is about to exit
+ * (i.e. this should be followed by a env->Exit() or an Abort()).
+ *
+ * Use enhance_stack = EnhanceFatalException::kDontEnhance
+ * when it's unsafe to call into JavaScript.
+ */
+static void ReportFatalException(Environment* env,
+                                 Local<Value> error,
+                                 Local<Message> message,
+                                 EnhanceFatalException enhance_stack) {
+  Isolate* isolate = env->isolate();
+  CHECK(!error.IsEmpty());
+  CHECK(!message.IsEmpty());
+  HandleScope scope(isolate);
 
-  AppendExceptionLine(env, er, message, FATAL_ERROR);
+  AppendExceptionLine(env, error, message, FATAL_ERROR);
+
+  auto report_to_inspector = [&]() {
+#if HAVE_INSPECTOR
+    env->inspector_agent()->ReportUncaughtException(error, message);
+#endif
+  };
 
-  Local<Value> trace_value;
   Local<Value> arrow;
-  const bool decorated = IsExceptionDecorated(env, er);
+  Local<Value> stack_trace;
+  bool decorated = IsExceptionDecorated(env, error);
 
-  if (er->IsUndefined() || er->IsNull()) {
-    trace_value = Undefined(env->isolate());
+  if (!error->IsObject()) {  // We can only enhance actual errors.
+    report_to_inspector();
+    stack_trace = Undefined(isolate);
+    // If error is not an object, AppendExceptionLine() has already print the
+    // source line and the arrow to stderr.
+    // TODO(joyeecheung): move that side effect out of AppendExceptionLine().
+    // It is done just to preserve the source line as soon as possible.
   } else {
-    Local<Object> err_obj = er->ToObject(env->context()).ToLocalChecked();
+    Local<Object> err_obj = error.As<Object>();
 
-    if (!err_obj->Get(env->context(), env->stack_string())
-             .ToLocal(&trace_value)) {
-      trace_value = Undefined(env->isolate());
+    auto enhance_with = [&](Local<Function> enhancer) {
+      Local<Value> enhanced;
+      Local<Value> argv[] = {err_obj};
+      if (!enhancer.IsEmpty() &&
+          enhancer
+              ->Call(env->context(), Undefined(isolate), arraysize(argv), argv)
+              .ToLocal(&enhanced)) {
+        stack_trace = enhanced;
+      }
+    };
+
+    switch (enhance_stack) {
+      case EnhanceFatalException::kEnhance: {
+        enhance_with(env->enhance_fatal_stack_before_inspector());
+        report_to_inspector();
+        enhance_with(env->enhance_fatal_stack_after_inspector());
+        break;
+      }
+      case EnhanceFatalException::kDontEnhance: {
+        report_to_inspector();
+        break;
+      }
+      default:
+        UNREACHABLE();
     }
+
     arrow =
         err_obj->GetPrivate(env->context(), env->arrow_message_private_symbol())
             .ToLocalChecked();
   }
 
-  node::Utf8Value trace(env->isolate(), trace_value);
+  node::Utf8Value trace(env->isolate(), stack_trace);
 
   // range errors have a trace member set to undefined
-  if (trace.length() > 0 && !trace_value->IsUndefined()) {
+  if (trace.length() > 0 && !stack_trace->IsUndefined()) {
     if (arrow.IsEmpty() || !arrow->IsString() || decorated) {
       PrintErrorString("%s\n", *trace);
     } else {
@@ -309,8 +353,8 @@ void ReportException(Environment* env,
     MaybeLocal<Value> message;
     MaybeLocal<Value> name;
 
-    if (er->IsObject()) {
-      Local<Object> err_obj = er.As<Object>();
+    if (error->IsObject()) {
+      Local<Object> err_obj = error.As<Object>();
       message = err_obj->Get(env->context(), env->message_string());
       name = err_obj->Get(env->context(), env->name_string());
     }
@@ -318,7 +362,7 @@ void ReportException(Environment* env,
     if (message.IsEmpty() || message.ToLocalChecked()->IsUndefined() ||
         name.IsEmpty() || name.ToLocalChecked()->IsUndefined()) {
       // Not an error object. Just print as-is.
-      String::Utf8Value message(env->isolate(), er);
+      String::Utf8Value message(env->isolate(), error);
 
       PrintErrorString("%s\n",
                        *message ? *message : "<toString() threw exception>");
@@ -337,10 +381,6 @@ void ReportException(Environment* env,
   }
 
   fflush(stderr);
-
-#if HAVE_INSPECTOR
-  env->inspector_agent()->FatalException(er, message);
-#endif
 }
 
 void PrintErrorString(const char* format, ...) {
@@ -406,7 +446,12 @@ namespace errors {
 TryCatchScope::~TryCatchScope() {
   if (HasCaught() && !HasTerminated() && mode_ == CatchMode::kFatal) {
     HandleScope scope(env_->isolate());
-    ReportException(env_, Exception(), Message());
+    Local<v8::Value> exception = Exception();
+    Local<v8::Message> message = Message();
+    if (message.IsEmpty())
+      message = Exception::CreateMessage(env_->isolate(), exception);
+    ReportFatalException(
+        env_, exception, message, EnhanceFatalException::kDontEnhance);
     env_->Exit(7);
   }
 }
@@ -771,6 +816,15 @@ void SetPrepareStackTraceCallback(const FunctionCallbackInfo<Value>& args) {
   env->set_prepare_stack_trace_callback(args[0].As<Function>());
 }
 
+static void SetEnhanceStackForFatalException(
+    const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  CHECK(args[0]->IsFunction());
+  CHECK(args[1]->IsFunction());
+  env->set_enhance_fatal_stack_before_inspector(args[0].As<Function>());
+  env->set_enhance_fatal_stack_after_inspector(args[1].As<Function>());
+}
+
 // Side effect-free stringification that will never throw exceptions.
 static void NoSideEffectsToString(const FunctionCallbackInfo<Value>& args) {
   Local<Context> context = args.GetIsolate()->GetCurrentContext();
@@ -785,7 +839,8 @@ static void TriggerUncaughtException(const FunctionCallbackInfo<Value>& args) {
   Local<Value> exception = args[0];
   Local<Message> message = Exception::CreateMessage(isolate, exception);
   if (env != nullptr && env->abort_on_uncaught_exception()) {
-    ReportException(env, exception, message);
+    ReportFatalException(
+        env, exception, message, EnhanceFatalException::kEnhance);
     Abort();
   }
   bool from_promise = args[1]->IsTrue();
@@ -799,6 +854,9 @@ void Initialize(Local<Object> target,
   Environment* env = Environment::GetCurrent(context);
   env->SetMethod(
       target, "setPrepareStackTraceCallback", SetPrepareStackTraceCallback);
+  env->SetMethod(target,
+                 "setEnhanceStackForFatalException",
+                 SetEnhanceStackForFatalException);
   env->SetMethodNoSideEffect(
       target, "noSideEffectsToString", NoSideEffectsToString);
   env->SetMethod(target, "triggerUncaughtException", TriggerUncaughtException);
@@ -847,6 +905,8 @@ void TriggerUncaughtException(Isolate* isolate,
   CHECK(!error.IsEmpty());
   HandleScope scope(isolate);
 
+  if (message.IsEmpty()) message = Exception::CreateMessage(isolate, error);
+
   CHECK(isolate->InContext());
   Local<Context> context = isolate->GetCurrentContext();
   Environment* env = Environment::GetCurrent(context);
@@ -873,7 +933,8 @@ void TriggerUncaughtException(Isolate* isolate,
   // during bootstrap, or if the user has patched it incorrectly, exit
   // the current Node.js instance.
   if (!fatal_exception_function->IsFunction()) {
-    ReportException(env, error, message);
+    ReportFatalException(
+        env, error, message, EnhanceFatalException::kDontEnhance);
     env->Exit(6);
     return;
   }
@@ -914,7 +975,9 @@ void TriggerUncaughtException(Isolate* isolate,
     return;
   }
 
-  ReportException(env, error, message);
+  // Now we are certain that the exception is fatal.
+  ReportFatalException(env, error, message, EnhanceFatalException::kEnhance);
+
   // If the global uncaught exception handler sets process.exitCode,
   // exit with that code. Otherwise, exit with 1.
   Local<String> exit_code = env->exit_code_string();